1. Field of the Invention
The present invention relates to a photomask material, a photomask and methods for the production thereof. More specifically, it relates to a photomask material for preparing a photomask for fabricating a circuit pattern, which mask is excellent in heat resistance, ultraviolet resistance and image strength and does not cause an environmental pollution, and a method for the production thereof, and it also relates to a photomask having the above properties and a method for the production thereof by a simple method.
2. Related Art Statement
Photomask are frequently used for forming circuit patterns in the production of semiconductor devices, liquid crystal display devices, and the like. The photomask for forming circuit patterns include an emulsion mask prepared by applying a photographic emulsion containing silver halide to a transparent substrate such as a film or a glass and a hard mask prepared by forming a light shielding film of a metal such as chromium, and these masks are generally used. In the emulsion mask, a photosensitive emulsion layer containing silver halide is irradiated with light, and an image is developed to form a black image. The emulsion mask using the above silver halide photography can be easily intensified in sensitivity, and the process for preparing the photomask is very easy. Since, however, the emulsion mask uses gelatin as a main binder for a photosensitive layer, it has defects that it is easily scratched when it is used a plurality of times as a contact photomask and that it is apt to be thermally deteriorated or colored due to heat generated by an exposure light source, or easily optically deteriorated and colored due to an ultraviolet light source.
In the hard mask, generally, a photoresist is applied to a glass substrate (blank) having a metal thin film as a light shielding film, followed by many steps of pre-baking, exposure, development, post-baking, descumming, etching, descumming, resist peeling and washing, to form an image. The hard mask is excellent in image strength, heat resistance and ultraviolet light durability. However, not only the steps of producing the photomask are complicated, but also the hard mask successfully attained no high sensitivity sufficient for a laser light source. Moreover, chromium is a main stream as a material for forming the light shielding film, and in recent years, it is demanded to employ other method eliminating an environmental problem caused by the use of chromium.
Besides the above method, further, as a method for preparing a photomask having a light shielding film formed of a metal thin film on a glass substrate, while using no organic binder such as gelatin, various methods have been proposed in which a silver halide photographic emulsion which can easily attain a high sensitivity is applied.
For example, U.S. Pat. No. 4,168,168 discloses a method in which a photosensitive material having a silver halide emulsion layer on a glass substrate, a so-called emulsion mask structure, is exposed and treated for development, then, the emulsion layer of an exposed portion or an unexposed portion is removed and silver ion or copper ion is supplied to form a metal image in a portion from which the emulsion layer has been removed. In the above heat treatment. U.S. Pat. No. 4,309,495 discloses a method in which a photosensitive material having the above emulsion mask structure is exposed and treated for development and then a developed silver is moved into a glass substrate by the application of a voltage and an increase in temperature, to form an image.
JP-B-53-2727, JP-B-60-41340, JP-A-6-273867, U.S. Pat. No. 3,960,560, U.S. Pat. No. 3,966,473, U.S. Pat. No. 4,113,486, U.S. Pat. No. 4,246,828 and U.S. Pat. No. 4,284,713 disclose methods in which a photosensitive material having a light shielding film formed of a metal or a metal oxide as a masking layer between a glass substrate and a silver halide emulsion layer is exposed and treated for development, a resist is formed on the light shielding film by an etch-bleaching or other method and is etched to peel a mask imagewise.
Further, JP-A-49-9975, JP-A-52-111382 and JP-A-57-26852 disclose methods in which a photosensitive material formed of a glass substrate, a mask layer, a photopolymer layer and a silver halide emulsion layer is exposed to photo-react the silver halide emulsion first, the silver halide emulsion layer is treated for development, then the material is exposed to photo-react the photopolymer and the photopolymer is treated for development and etched, to peel a mask imagewise.
As described above, the above conventional methods of forming a metal thin film by applying a silver halide emulsion requires complicated steps of exposure, heating after development, etching, application of a voltage, and the like, and there is desired a photomask having a light shielding film formed of a metal thin film on a glass substrate, which can be produced by a simple method.